Configuration and dynamics of hydride ions in the nitride-hydride catalyst CaCrNH

Fine, L.*; Lavn, R.*; Wei, Z.*; 津森 竜也*; 陰山 洋*; 梶本 亮一; Jimenz-Ruiz, M.*; Koza, M. M.*; Karlsson, M.*

Chemistry of Materials, 37(1), p.489 - 496, 2024/12

https://doi.org/10.1021/acs.chemmater.4c02897

We report results on the configuration and vibrational dynamics of hydride-ions (H) in the novel nitridehydride catalyst CaCrNH, by means of variable temperature inelastic neutron scattering (INS) experiments, harmonic phonon calculations, and machine-learning molecular dynamics (MLMD) calculations. The combined analyses of experimental and theoretical data show that the vibrational dynamics of H are manifested as a broad, asymmetric vibrational band between 80 and 130 meV. Crucially, these modes are polarized along the crystallographic axis, and their dispersive character reveals significant interactions between neighbouring H in the material. We find that most H are surrounded by two other H and that the H sites of the studied sample have an occupancy of at least 95%. We argue that this high H occupancy may be related to the material's high efficiency as a catalyst for ammonia synthesis.